There have been proposed various fluidized-bed gasification furnaces for producing decomposition gas, using solid fuel such as coal or organic waste as fuel. One of such fluidized-bed gasification furnaces is called synthesized gasification furnace which comprises gasification and char combustion chambers each of which is supplied at its bottom with fluidizing gas to provide a fluidized bed, said chambers being partitioned by a partition wall with a bottom opening and being integrally configured as a whole. Bed material is circulated between the chambers via the opening on the partition wall; char (flammable solid content) is entrained in and conveyed by the bed material from the gasification chamber to the char combustion chamber, and the bed material having been heated by burning the char (flammable solid content) in the char combustion chamber is transferred from the char combustion chamber to the gasification chamber (see, for example, Reference 1).
In the device shown in Reference 1, the gasification and char combustion chambers are arranged side by side with the single partition therebetween, part of the flammable solid content produced in the gasification chamber being guided through the opening into and burned in the combustion chamber. However, movement of the flammable solid content from the gasification chamber to the char combustion chamber is drifting or catch-as-catch-can basis and may disadvantageously be extremely unstable. To overcome this, there are provided in Reference 1 highly and low fluidized regions with high and low fluidizing-gas superficial velocities so as to control fluidization of the flammable solid content. However, even if the superficial velocities are controlled in this manner, it is impossible to effectively feed only the flammable solid content having been sufficiently gasified in the gasification chamber to the char combustion chamber; thus, the flammable solid content is fed to the char combustion chamber with part of the flammable solid content being insufficiently gasified. As a result, in a case where gasification fuel is high fuel ratio fuel such as coal having fixed carbon content in large quantity, or fuel (organic waste, mixed fuel or the like) mingled with high fuel ratio raw material having fixed carbon content in large quantity, there is a problem that high gasification efficiency cannot be obtained since effective arrestment in the gasification chamber of only the flammable solid content derived from the high fuel ratio fuel cannot be conducted for promotion of gasification.
In order to overcome the problems in Reference 1, the applicant proposed a device for gasifying gasification fuel (see Reference 2), using an external circulation type combustor.
FIG. 1 schematically shows a gasification device which uses the combustor of Reference 2 to generate useful flammable gas from gasification fuel. The gasification device comprises a combustion furnace 1 for mainly burning flammable solid content and a gasification furnace 2 for mainly gasifying gasification fuel. To a lower part of the combustion furnace 1, air 3 and starting fuel 4 such as city gas, kerosene or heavy oil are fed and are burned in mixture while being bubbled with bed material such as sand, whereby a fluidized bed 5 is formed for heating of bed material; further, a high-temperatured freeboard 6 is formed in the combustion furnace 1 and above the fluidized bed 5. Shown in FIG. 1 is an air diffuser plate 7 through which the air 3 is blown into the furnace 1 for formation of the fluidized bed 5; alternatively, a conventionally employed air diffusing nozzle may be used for blowing the air 3 into the furnace 1 for formation of the fluidized bed 5. Supply of the starting fuel 4 is reduced as gasification fuel 12 is supplied as mentioned below; the supply of the starting fuel is eventually stopped.
A top of the combustion furnace 1 is connected with an exhaust gas pipe 8. Exhaust gas discharged through the pipe 8 is guided into a material separator 9 (hot cyclone) for separation of bed material 10 entrained in the gas. The bed material 10 separated in the separator 9 is supplied through a material downcomer 11 into the gasification furnace 2.
A top of the gasification furnace 2 has a fuel supply port 13 through which fed is gasification fuel 12 such as fuel like coal or coke having fixed carbon content in large quantity (hereinafter referred to as high fuel ratio fuel), organic waste such as various waste or sludge, or combination thereof. A bottom of the gasification furnace is fed with steam 14, the steam 14, high-temperatured bed material 10 and gasification fuel 12 being bubbled together to form a fluidized bed 15; the gasification fuel 12 is gasified by the high-temperatured bed material 10. Shown in FIG. 1 is an air diffuser plate 7a through which the steam 14 is blown into the furnace 2 for formation of the fluidized bed 15; alternatively, a conventionally employed air diffusing nozzle may be used for blowing the steam 4 into the furnace 2 for formation of the fluidized bed 15.
Flammable gas 16 generated by gasifying the gasification fuel 12 is taken out through an output port 17 on the top of the gasification furnace 2. The flammable gas 16 is supplied to a utilization device such as a turbine for power generation.
Flammable solid content 18 also generated by gasifying the gasification fuel 12 in the furnace 2 is gradually pushed and moved from right side to left side in FIG. 1 by the bed material 10 continuously fed through the downcomer 11, and is supplied in a mixed state with the bed material 10 to the combustion furnace 1 through a solid content supply port 19 which connects, with declivity, a heightwise intermediate portion of a left side end of the gasification furnace 2 to the combustion furnace 1.
In the gasification device, the gasification fuel 12 supplied through the supply port 13 into the gasification furnace 2 is heated by the high-temperatured bed material 10 and contacts the steam 14 to bring about aqueous gasification reaction (C+H2O=H2+CO), whereby the flammable gas 16 such as CO and H2 are generated together with flammable solid content 18. The generated flammable gas 16 is fed through the output port 17 of the furnace 2 to a utilization device (not shown) such as a turbine for power generation.
On the other hand, the flammable solid content 18 generated in the gasification furnace 2 is moved from one side (right side) to the other side (left side) in FIG. 1 by the bed material 10 continuously fed through the downcomer 11 and is fed together with the bed material 10 into the combustion furnace 1 through the supply port 19 on the left side end of the furnace 2. The supplied flammable solid content 18 is burned in the fluidized bed 5 to elevate in temperature the combustion gas and bed material in the combustion furnace 1. Exhaust gas 20 separated in the separator 9 is exhausted to atmosphere via an exhaust heat recovery device such as a boiler, an exhaust gas treatment device and the like (not shown).
[Reference 1] JP 2004-196831A
[Reference 2] JP 2006-132885A